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Methane tracer possible option for gas drilling

Use of a tracer additive could help establish whether methane in water wells in places such as Garfield County is connected to oil and gas development, a hydrologist with the U.S. Geological Survey says.

Judith Thomas made the observation Thursday in an interview after her presentation to the Garfield County Energy Advisory Board on two new USGS reports reviewing more than a half-century worth of ground and surface water quality data in western Colorado’s Piceance Basin.

The report notes that methane testing results were available for 874 wells, primarily in Garfield County, and it was detected in 24 percent of those wells. Most methane detections and high-methane concentrations were in the Mamm Creek-Divide Creek area south of Silt and Rifle.

But Thomas noted that there’s a dearth of methane testing data available in other areas, meaning that “we wouldn’t know” whether it’s just a localized occurrence.

Determining whether gas development contributed to it also is made more difficult because of a lack of predevelopment testing to show if methane already existed in the water, she said.

Isotopic data is available in the case of 37 samples showing high methane levels, and that data indicated the methane in the Garfield wells was from both biogenic and thermogenic sources. Biogenic methane results from microbial degradation of organic matter, whereas thermogenic gas is produced from heat and pressure, generally far below freshwater aquifers, in formations targeted for drilling.

But Thomas noted that even thermogenic gas can reach domestic well water through natural pathways rather than drilling in areas with a lot of geological faults and fractures, such as Mamm/Divide creek.

“There’s no further information in the data that tells us where it might be coming from,” she said. “It would need almost a distinct tracer that would be specific only to (oil and gas) development.”

Some have advocated for tracer additives in hydraulic fracturing fluids.. Thomas said the USGS is part of a group that includes industry working on adding tracers to fracking fluid in Pennsylvania, partly to look at the possibility of methane migration to well water.

“We don’t have a group doing that out here in Colorado. … It’s a real limitation without a distinct tracer that’s specific to gas development.”

She said the USGS has proposed doing a study in the Yellow Creek area outside Meeker to look for thermogenic methane in shallow groundwater before drilling has occurred.

No drinking-water standards apply to methane, but it can reach explosive levels in confined spaces.

Thomas said the explosion danger occurs when methane exceeds 28 milligrams per liter. The highest detection in the samples included in the USGS report was 36.7 milligrams per liter. In 75 samples, methane topped 1 milligram per liter.

Findings in the latest phase of a Garfield County hydrology study looking at groundwater methane in the Mamm/Divide creek area could be released later this year.